Conventionally, a user of a vehicle searches for and finds the parking spot in which his/her vehicle is parked in a large parking garage by operating a predetermined button (e.g., a panic button, a lock-unlock button) of a communication device that is carried by the user. The communication device then sends a predetermined car finder signal (e.g., a panic signal, a lock/unlock signal). In response, an in-vehicle device installed in the vehicle receiving the car finder signal from the communication device performs a predetermined answerback operation (e.g., blinking of a hazard lamp, blowing of a buzzer or a horn) as a notification. For instance, Japanese Patent Laid-Open No. 2007-241472 (JP '472) discloses such a technique. Such a function is designated as a car finder function.
In such a conventional system, one answerback operation in response to a reception of the car finder signal ends rather quickly. Therefore, it may be necessary for the user to repeat the operation by operating the predetermined button of the communication device many times until he/she finally finds the vehicle when the user walks around in search of the vehicle in, for example, the parking garage, which is cumbersome. Further, it may be difficult for the user to repeat the same operation on the communication device in a situation where the user's hands are occupied, for instance, by luggage or holding a child.